Industrial robots have become an indispensable part of modern manufacturing. Whether transferring semiconductor wafers from one process chamber to another in a cleanroom or cutting and welding steel on the floor of an automobile manufacturing plant, robots perform many manufacturing tasks tirelessly, in hostile environments, and with high precision and repeatability.
In many robotic manufacturing applications, it is cost-effective to utilize a relatively generic robot arm to accomplish a variety of tasks. For example, in an automotive manufacturing application, a robot arm may be utilized to cut, grind, or otherwise shape metal parts during one phase of production, and perform a variety of welding tasks in another. Different welding tool geometries may be advantageously mated to a particular robot arm to perform welding tasks at different locations or in different orientations.
In these applications, a tool changer is used to mate different robotic tools to the robot. One half of the tool changer, called the master unit, is permanently affixed to a robot arm. The other half, called the tool unit, is affixed to each robotic tool that the robot may utilize. The various robotic tools a robot may utilize are typically stored, within the range of motion of the robot arm, in tool stands which are sized and shaped to hold each tool securely when not in use. When the robot arm positions the master unit, on the end of the robot arm, adjacent to a tool unit connected to a desired robotic tool sitting in a tool stand, a coupling mechanism is actuated that mechanically locks the master and tool units together, thus affixing the robotic tool to the end of the robot arm. The tool changer thus provides a consistent mechanical interface between a robot arm and a variety of robotic tools. A tool changer may also pass utilities, such as electrical current, air pressure, hydraulic fluid, cooling water, electronic or optical data signals, and the like, to a robotic tool.
A variety of coupling mechanisms are known in the art of robotic tool changers. One simple, reliable, scalable mechanism comprises a piston moveable along a longitudinal axis, with a plurality of rolling members, such as balls or cylinders, disposed radially around the piston—either interior or exterior to the piston. As the piston advances from a retracted to an extended position, an angled surface of the piston contacts the rolling members, urging them either inwardly or outwardly as the piston advances. The piston and rolling members may be disposed on one unit of the tool changer, such as the master unit. As the rolling members are displaced by the piston, they contact an angled surface in the other unit, such as the tool unit. Pressure on the angled surface locks the tool unit to the master unit, until the piston is retracted and pressure on the rolling members is relieved.
In this type of coupling mechanism, continuous motive force must be provided, driving the piston toward the extended position, to keep the tool unit locked to the master unit. This force may, for example, be provided by mechanical springs, pneumatic pressure, or the like. When springs are used, a large force must be applied to retract the piston, against the force of the springs, when decoupling the tool unit from the master unit. Such decoupling force may be excessive for hand-actuated tool changers. In tool changers that use pneumatic fluid to drive the piston, a constant source of pneumatic fluid must be provided. Any failure of the pneumatic source, supply lines, O-rings, or the like may result in loss of pressure, presenting a safety hazard as the tool unit (and attached tool) may become decoupled from the master unit (and hence from the robot).
A need exists in the art for a coupling mechanism for a robotic tool changer, which applies a strong, continuous, failure-proof motive force to a piston while coupled, but which may be decoupled without requiring the application of a large force. For safety, as well as reduced cost, complexity, weight, and the like, the motive force should not require an external source of power, or coupling between an external power source and tool changer coupling mechanism.
The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.